scholarly journals Effect of Dopamine Loss and the Metabolite 3-O-Methyl-[18F]Fluoro-dopa on the Relation between the 18F-Fluorodopa Tissue Input Uptake Rate Constant Kocc and the [18F]Fluorodopa Plasma Input Uptake Rate Constant Ki

2003 ◽  
Vol 23 (3) ◽  
pp. 301-309 ◽  
Author(s):  
V. Sossi ◽  
J. E. Holden ◽  
R. de la Fuente-Fernandez ◽  
T. J. Ruth ◽  
A. J. Stoessl
Keyword(s):  
Rate Constant ◽  
Uptake Rate ◽  
Dopaminergic Neurons ◽  
Storage Capacity ◽  
Synthesis Rate ◽  
Positron Emission ◽  
Uptake Rate Constant ◽  
Downward Bias ◽  
Storage Rate ◽  
And Storage

Parkinson disease is characterized by the loss of dopaminergic neurons, thus decreasing the system's ability to produce and store dopamine (DA). Such ability is often investigated using 18F-fluorodopa (FD) positron emission tomography. A commonly used model to investigate the DA synthesis and storage rate is the modified Patlak graphical approach. This approach allows for both plasma and tissue input functions, yielding the respective uptake rate constants Ki and Kocc. This method requires the presence of an irreversible compartment and the absence of any nontrapped tracer metabolite. In the case of Kocc, this last assumption is violated by the presence of the FD metabolite 3- O-methyl-[18F]fluoro-dopa (3OMFD), which makes the Kocc evaluation susceptible to a downward bias. It was found that both Ki and Kocc are influenced by DA loss and thus are not pure measures of DA synthesis and storage. In the case of Kocc, the presence of 3OMFD exacerbates the effect of DA egress, thus introducing a disease-dependent bias in the Kocc determination. These findings imply that Ki and Kocc provide different assessments of disease severity and that, as disease progresses, Ki and especially Kocc become more related to DA storage capacity and less to the DA synthesis rate.

scholarly journals α[C-11]Methyl-l-Tryptophan PET Maps Brain Serotonin Synthesis and Kynurenine Pathway Metabolism

2000 ◽  
Vol 20 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Diane C. Chugani ◽  
Otto Muzik
Keyword(s):  
Rank Order ◽  
Kynurenine Pathway ◽  
Tracer Uptake ◽  
Synthesis Rate ◽  
Serotonin Synthesis ◽  
Serotonin Content ◽  
Disease States ◽  
Positron Emission ◽  
Glucose Metabolic Rate ◽  
Uptake Rate Constant

α[C-11]Methyl-l-tryptophan (AMT) is an analog of tryptophan used with positron emission tomography for the measurement of serotonin synthesis in humans. Several attempts have been made to estimate the serotonin synthesis rate from plasma and brain kinetic data of AMT using the same model as that applied for the measurement of the glucose metabolic rate with 2-deoxyglucose. However, although AMT is similar to 2-deoxyglucose with regard to an irreversible pool of tracer uptake, there are important differences between the two tracers and how the model can be applied. These differences include transport at the blood-brain barrier and the presence of a large unmetabolized pool of AMT, precluding the method from providing the absolute serotonin synthesis rate. Despite this limitation, the unidirectional uptake rate constant (K-complex) values have been found to be stable within an individual, and the rank order of regional brain values for K-complex are consistent with the rank order for serotonin content in human brain. Furthermore, changes in K-complex with age, gender, and disease states are consistent with previously reported biochemical measurements of serotonin in brain tissue. The authors suggest, therefore, that the K-complex is an index of serotonin synthesis which they have termed the “serotonin synthesis capacity.” The authors argue that AMT is a useful tracer for study of serotonergic mechanisms, and under certain pathologic states, of metabolism by means of the kynurenine pathway.

Orthophosphate Uptake Rate Constants are Mediated by the 103–104 Molecular Weight Fraction in Shield Lake Waters

1984 ◽  
Vol 41 (1) ◽  
pp. 166-173 ◽  
Author(s):  
P. Brassard ◽  
J. C. Auclair
Keyword(s):  
Molecular Weight ◽  
Rate Constant ◽  
Uptake Rate ◽  
External Solution ◽  
Phosphorus Compounds ◽  
Phytoplankton Assemblages ◽  
Physiological Basis ◽  
Colloidal Phosphorus ◽  
Uptake Rate Constant ◽  
Lake Waters

Although midsummer chlorophyll concentrations can be predicted from total phosphorus, attempts to identify all bioavailable phosphorus compounds has proven difficult. Inconsistencies in determining colloidal phosphorus utilization and the discovery that orthophosphate concentration and flux are poor predictors of lake trophic status has led us to postulate that other forms of phosphorus compounds, which may not be necessarily labeled over the radioisotopic uptake assay (32P) period, are assimilated by natural phytoplankton assemblages. Using ultrafiltration methodology we test the hypothesis that the orthophosphate uptake rate constant can be physiologically varied upon changing the external concentration of selected molecular weight fractions in Shield lake waters. We determined that the fraction between molecular weight 103 and 104 significantly increased the orthophosphate uptake rate constant when exposed to the natural seston. Our discovery suggests that the orthophosphate uptake rate constant is subject to fluctuations depending on the availability of low molecular weight phosphorus metabolites in the external solution. The physiological basis of our observations may be a metabolic coupling between the activity of plasmalemma-bound phosphatases and the transport of PO43− across the cell membrane.

Uptake of monohydric alcohols by liver: demonstration of a shared enzymic space

1983 ◽  
Vol 244 (2) ◽  
pp. G198-G214
Author(s):  
C. A. Goresky ◽  
E. R. Gordon ◽  
G. G. Bach
Keyword(s):  
Rate Constant ◽  
Uptake Rate ◽  
Removal Rate ◽  
Hepatic Uptake ◽  
Multiple Indicator Dilution ◽  
Ethanol Infusion ◽  
Monohydric Alcohols ◽  
Uptake Rate Constant ◽  
Anesthetized Dogs ◽  
Steady State Levels

Multiple-indicator dilution studies of the hepatic uptake of straight-chain C1-C5 monohydric alcohols were carried out in anesthetized dogs, with either no preceding or saturating infusions of ethanol, and at different steady-state levels for the C2 experiments. Labeled red cells were utilized as a vascular reference, and labeled water was used as a second reference entering liver cells. Kinetic analysis of the data provided estimates of both an uptake rate constant and the space of distribution available to label. From the decrease in the uptake rate constant for labeled ethanol with bulk concentration, we calculated a maximal removal rate of 0.025 mumol X s-1 X (ml liver water)-1 and a Michaelis constant (Km) of 0.32 mM. Especially for the labeled C3-C5 alcohols, a space in excess of that available to water was found, and the bulk of this was dissipated by ethanol infusion. The increment, the "shared enzymic space", which varies with enzymic concentration and inversely with Km, was used to calculate Km values for the other alcohols.

Chemical and Radiotracer Measurements of Phosphorus Uptake by Lake Plankton

1983 ◽  
Vol 40 (2) ◽  
pp. 147-155 ◽  
Author(s):  
D. R. S. Lean ◽  
E. White
Keyword(s):  
Rate Constant ◽  
Lake Water ◽  
Uptake Rate ◽  
Phosphorus Uptake ◽  
Small Cells ◽  
Phosphate Limitation ◽  
Isotope Method ◽  
Uptake Rate Constant ◽  
Ambient Concentrations ◽  
Uptake Velocity

Either chemical or radioisotope methods can be used to measure the maximum uptake velocity for phosphorus in lake water but neither can measure uptake at ambient concentrations. Chemical estimates at ambient concentrations are insensitive and the isotope method provides the uptake rate constant only. By multiplying the uptake rate constant by the ambient phosphate concentration one obtains an estimate for phosphorus influx, but reliable estimates for ambient phosphate concentrations are still unattainable. At added phosphate levels even up to 10 μg P∙L−1, the isotope method overestimates net phosphate uptake because of release of phosphate from the plankton. Influx and efflux are practically equal under steady state conditions, and during periods of phosphate limitation a net uptake of phosphorus occurs only when there is an increase in the phosphorus supply. The uptake of phosphate is predominantly by small cells at low concentrations of added phosphate and by larger cells at the higher enrichments. This makes the use of the radiobioassay for estimating ambient phosphate concentrations difficult to interpret. Furthermore the half-saturation coefficients measured for whole lake water are a mean for the entire population and consist of small values for small algae and bacteria and larger values for larger algae.Key words: phosphorus, kinetics, plankton, algae, bacteria nutrition

scholarly journals A Reversible Tracer Analysis Approach to the Study of Effective Dopamine Turnover

2001 ◽  
Vol 21 (4) ◽  
pp. 469-476 ◽  
Author(s):  
Vesna Sossi ◽  
Doris J. Doudet ◽  
James E. Holden
Keyword(s):  
Rate Constant ◽  
Input Function ◽  
Dopamine Turnover ◽  
Disease States ◽  
Positron Emission ◽  
Alternative Approach ◽  
Uptake Rate Constant ◽  
Kinetic Component ◽  
Specific Uptake ◽  
Kinetics Of

Changes in dopamine turnover resulting from disease states such as Parkinson's disease may be reflected in corresponding changes in the kinetics of the positron emission tomographic tracer [18F]fluorodopa. The authors had previously refined the conventional irreversible-tracer graphical approach to determine both the uptake rate constant Ki and the rate constant kloss that describes the slow loss of the trapped kinetic component. Because these parameters change in the opposite sense with disease, their ratios may be more powerfully discriminating than either one alone. The ratio kloss/Ki is indicative of effective dopamine turnover. Its inverse, Ki/kloss, can be interpreted as the effective distribution volume (EDV) of the specific uptake compartment referred to the fluorodopa concentration in plasma. Here the authors present a new approach to the estimation of EDV based on reversible-tracer graphical methods. When implemented with a plasma input function, the method evaluates EDV directly. When implemented with a tissue input function, the outcome is proportional to the ratio of the distribution volumes of the specific uptake and precursor compartments. Comparison of the new and previous approaches strongly validates this alternative approach to the study of effective dopamine turnover.

Uptake from Seawater and Clearance of p,p′-DDT by Marine Planktonic Crustacea

1979 ◽  
Vol 36 (3) ◽  
pp. 247-254 ◽  
Author(s):  
Gareth C. H. Harding ◽  
W. Peter Vass
Keyword(s):  
Surface Area ◽  
Rate Constant ◽  
Uptake Rate ◽  
Rate Constants ◽  
Clearance Rate ◽  
Dry Weight ◽  
Exponential Model ◽  
Uptake Rate Constant ◽  
Clearance Rate Constant ◽  
Planktonic Crustaceans

A simple exponential model is used to interpret the simultaneous uptake and clearance of p,p′-DDT by euphausiids and copepods to and from seawater,[Formula: see text]where [C] and [W] are the concentrations in the organism and seawater, respectively. The clearance rate constant for euphausiids, kj = 0.043/d, is not significantly different from that observed for copepods, 0.048/d. No trend in ki values is detected over the range of p,p′-DDT concentrations in seawater used, 27.8–1388 ng/L. Furthermore, there is a great deal of overlap in the uptake rate constant values between organisms. Uptake rate constants range from 0.76 to 1.21 × 104/d for euphausiids and from 1.04 to 2.51 × 104/d for copepods. There appears to be no need to use a surface-area term if the concentration of p,p′-DDT in the organism is expressed per unit dry weight even though the euphausiids are 2 orders of magnitude larger than copepods. Knowing levels of ΣDDT present in planktonic crustaceans in nature, back calculations suggest that there must be [Formula: see text] ΣDDT/L in seawater. A considerable amount of the ΣDDT reported in seawater must therefore be unavailable to plankters because it is "bound" to particles. Key words: p,p′-DDT, uptake, clearance, surface area, euphausiids, copepods

Uptake Rate Constant

2016 ◽  
Author(s):  
Monica Nordberg ◽  
Douglas M. Templeton ◽  
Ole Andersen ◽  
John H. Duffus
Keyword(s):  
Rate Constant ◽  
Uptake Rate ◽  
Uptake Rate Constant

scholarly journals Kemampuan Kerang Hijau (Perna viridis) Mengakumulasi Plutonium Melalui Jalur Air Laut

2019 ◽  
Vol 5 (1) ◽  
Author(s):  
Budiawan Budiawan ◽  
Nur Hidayati Febriana ◽  
Heny Suseno
Keyword(s):  
Rate Constant ◽  
Release Rate ◽  
Uptake Rate ◽  
Bioconcentration Factor ◽  
Perna Viridis ◽  
Nuclear Facilities ◽  
Run Off ◽  
Uptake Rate Constant ◽  
Biokinetic Parameters ◽  
Non Parametric

Operasional fasilitas nuklir yang ada di Serpong memungkinkan melepas radionuklida ke lingkungan. Isotop Pu merupakan radionuklida yang terlepas ke lingkungan. Lepasan tersebut terbawa oleh air sungai atau run off memasuki Teluk Jakarta. Kerang hijau (Perna viridis) mampu mengakumulasi radionuklida tersebut. Studi ini bertujuan untuk memahami kinetika proses bioakumulasi Pu oleh kerang hijau yang dipengaruhi oleh spesiasinya. Percobaan dilakukan melalui tahapan: aklimatisasi, bioakumulasi (242Pu3+ dan 242Pu4+) dan depurasi. Parameter biokinetika diamati meliputi faktor konsentrasi (CF), konstanta laju pengambilan (ku), konstanta laju pelepasan (ke), faktor biokonsentrasi (BCF), dan waktu paruh biologis (tb1/2). Berdasarkan uji statis non parametric menunjukkan spesiasi 242Pu3+ dan 242Pu4+ berpengaruh terhadap kemampuan Perna viridis mengakumulasi Pu.  Rerata kemampuan bioakumulasi 242Pu4+  oleh Perna viridis adalah 1,2 kali dibandingkan 242Pu4+. Kata kunci : Bioakumulasi , biokinetika,  Perna viridis, plutonium,  spesiasi,  Perna viridis, plutonium. Operations of nuclear facilities in Serpong have potentially release radionuclides to environment. Pu isotope is one of radionuclide that is released into the environment. The release of this radionuclide was carried by the river water or run off entered the Bay of Jakarta. Green mussels (Perna viridis) can be accumulate this radionuclides. The aims of this study was to understand of the biokinetic of Pu bioaccumulation process by green mussels which are affected by its speciation. The experiment was carried out through stages: acclimatization, bioaccumulation (242Pu3+ and 242Pu4+) and depuration. Biokinetic parameters was observed include concentration factor (CF), uptake rate constant (ku), release rate constant (ke), bioconcentration factor (BCF), and biological half-life (tb1/2). Base on non parametric statistic test shown that speciation of 242Pu3+ and 242Pu4+ had an effect on the ability of Perna viridis to accumulate Pu. Avarage of bioaccumulation capabilities of 242Pu4+ by Perna viridis are 1.2 than 242Pu3+. Keywords: bioaccumulation, biokinetics, plutonium, Perna viridis,  speciation.

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